The present invention relates to a shift selector mechanism for use in vehicles with an automatic transmission having no park setting.
The most commonly used shift selector mechanism for passenger automobiles utilizes a shift selector with one or more drive positions, a reverse position, a neutral position and a park position. Selection of the park position places the automatic transmission into its park setting. In the park setting, the transmission output shaft is locked by means of a pawl or sprag, thereby preventing the vehicle from moving. Most medium and heavy duty vehicles having automatic transmissions, on the other hand, are equipped with transmissions having no park setting, because the loads are such that it is not practical to lock and unlock the larger transmissions in this fashion. Consequently, vehicles with such transmissions have shift selectors with no park position. This situation causes no problem for those used to driving such vehicles. In order to park the vehicle, the driver simply moves the shift handle to the neutral position and sets the vehicle brakes.
Not all drivers of medium and heavy duty vehicles with automatic transmissions are familiar with such transmissions, however. Unfamiliarity is particularly common among drivers of rental trucks and school buses. Absence of a park position may confuse a driver used to passenger vehicles having a shift selector park position and unfamiliar with vehicle shift selectors having no park position. The inexperienced driver may choose to place the shift handle into one of the drive or reverse positions when parking the vehicle. This choice tends to cause clutch/band load and wear. Some drivers may even select the dangerous alternative of moving the shift lever to neutral but then fail to apply the parking brake.
It has been suggested that, for such automatic transmissions not having a park position, there is a need for a system of returning the transmission to neutral and applying the vehicle park brake when a shift selector is moved into a park position. Such a system will prevent confusion of the driver unfamiliar with shift selector mechanisms having no park position and will minimize transmission clutch/band load caused by use of a drive or reverse gear when parked, and minimize risk of an unsafe, no-brake-applied condition.